1. Field of the Invention
The present invention relates to a signal transmission device for a towing vehicle and more particularly, to a signal transmission device, which utilizes a magnetic attractive force to fasten the electrical connectors at the two ends of a cable to the truck-tractor and trail of towing vehicle respectively and, which allows quick mounting and dismounting of the electrical connectors.
2. Description of the Related Art
A towing vehicle uses a truck-tractor to pull a trailer, semi-trailer, platform or container platform. The cart (trailer, semi-trailer, platform or container platform) to be pulled is provided at the rear side of the truck-tractor and linked thereto by a coupling. The coupling is a mechanical linking mechanism that allows the truck-tractor to pull the card and to turn the card when the truck-tractor is turning, shortening the turn radius of the towing vehicle. The coupling simply provides a mechanical link, cannot transmit electric signals.
Subject to traffic regulations for safety parts, the cart to be pulled by a truck-tractor must be equipped with directional lights, stoplights, and parking lights. These signal lights must be controlled by the truck-tractor so that the driver in the truck-tractor can operate related switches to turn on/off these signal lights. Therefore, a cable must be arranged between the truck-tractor and the cart linked to the track-tractor for transmission of electric signals.
Further, an advanced truck-tractor may be installed therein a monitoring system to monitor the operation status of the cart being pulled. The status signals and data generated by this monitoring system must be transmitted to the truck-tractor. For example, a TMPS (Tire Pressure Monitoring System) has sensors installed in the wheels of the towing vehicle to detect the tire pressure of the wheels and to transmit the respective detected tire pressure signal by radio. However, because of low power level, the radio signal must be filtered and amplified by a receiver circuit in the cart that is pulled by the truck-tractor and then transmitted by the receiver circuit through a cable to the console in the truck-tractor.
Therefore, a cable must be provided between the truck-tractor and the cart being pulled by the truck-tractor to achieve signal transmission. However, the connection between the truck-tractor and the cart must be easily detachable so that another cart can be switchingly connected to the truck-tractor. For example, when the truck-tract of a container truck pulled the container with the container platform from the start point to the destination, the container platform must be immediately disconnected from the truck-tractor so that an empty container platform can be connected to the truck-tractor and then pulled by the truck-tractor to the start point again for exchange of the empty container platform with another container platform that carries another container for a next transportation. During connection and disconnection between the truck-tractor and the attached cart, the cable must be relatively connected and disconnected.
For quick connection of a cable between a truck-tractor and a cart to be pulled by the truck-tractor according to a conventional method, an electrical female connector is respectively and fixedly provided at the truck-tractor and the cart to be pulled by the truck-tractor, and the two opposite ends of the cable are respectively provided with an electrical male connector. By means of detachably connecting the electrical male connectors to the electrical female connectors, the cable is quickly and detachably connected between the truck-tractor and the cart. When the truck-tractor changes the moving direction, the distance between the two electrical female connectors is relatively increased, causing the cable to be stretched. To avoid disconnection of the electrical male connectors from the electrical female connectors when the cable is being stretched, means for preventing disconnection may be provided to enhance the connection between the respective electrical male connectors and the respective electrical female connectors. According to conventional methods, a locking device is provided at each electrical female connector for locking the associated electrical male connector. Taiwan Utility Model Nos. 478457 and M246643, U.S. Pat. No. 7,258,559 and publication No. 2007072461 teach the use of different fixation means to lock the electrical male connector, keeping positive connection between the electrical male connector and the matched electrical female connector. Further, U.S. Pat. No. 7,172,150 discloses a retractable reel apparatus for connecting the electrical wiring on a trailer to the electrical system of a towing vehicle. This design allows adjustment of the connection length of the electrical wiring to fit straight movement or turning of the truck-tractor.
However, the use of lock means to lock an electrically female connector to an electrical male connector simply prohibits movement of the electrical male connector in direction away from the electrical female connector. When stretched by an external force (stretched by the cable), the electrical male connector will be vibrated with the cable. A severe vibration of the electrical male connector may cause a contact error or damage to the electrical female connector. Further, when the cable is frequently stretched, the electrical male connector may be kept connected to the electrical female connector by the lock means, however the electrical contacts between the cable and contact pins of the electrical male connector may be damaged, losing the signal transmission function of the cable.